1. Field of the Invention
The present invention relates to a phase shifter for shifting the phase of signals propagating on a transmission line, and to a phased-array antenna and radar incorporating the phase shifter.
2. Description of the Related Art
A typical phase shifter for shifting the phase of electromagnetic waves propagating on a transmission line includes a dielectric plate which is positioned with respect to a waveguide so as to be freely insertable into the waveguide.
In an exemplary phased-array antenna including arrays of a plurality of slot antennas, a movable spacer plate can be moved back and forth to control feed phase with respect to each of the slot antennas to perform beam scanning.
However, such typical phase shifters or phased-array antennas have the following problems.
Since a typical phase shifter controls the phase by adjusting the amount by which the dielectric plate is inserted into the waveguide, for example, it is necessary to move the dielectric plate back and forth in order to periodically change the phase. The structure which facilitates the back-and-forth movement of the dielectric plate makes it difficult to maintain high mechanical reliability, and also makes it difficult to move the dielectric plate back and forth at high speed.
Furthermore, there has been no example in which a typical phase shifter is applied to a transmission line, such as a microstrip line, formed on a dielectric plate or a dielectric line formed by placing a dielectric strip between two metal plates.
A typical phased-array antenna requires a removable spacer plate to be moved back and forth in order to control feed phase with respect to a plurality of slot antennas, and it is difficult to control the phase at high speed.
Accordingly, it is an object of the present invention to provide a phase shifter capable of periodically controlling phase at high speed and formed of a planar transmission line such as a microstrip line or a dielectric line. Another object of the present invention is to provide a phased-array antenna which uses the phase shifter to achieve rapid beam scanning with a simplified overall structure, and to provide a radar which uses the phased-array antenna to quickly change the radar coverage range.
To this end, the present invention provides a phase shifter including a substantially planar dielectric plate, a conductive strip formed on the dielectric plate, and a rotator at least partially including a conductor and a dielectric, the rotator being positioned in proximity to the conductive strip so as to freely rotate.
Therefore, the conductive strip on the dielectric plate can serve as a planar transmission line such as a microstrip line. As the rotator rotates, the distance from the conductor or dielectric of the rotator to the conductive strip or the opposing areas changes, thereby changing the phase constant of the planar transmission line, thus causing a change in the phase of a signal propagating on the transmission line. The signal propagating on the transmission line changes in phase as the rotator rotates, thereby reducing the product of mass and acceleration (inertia resistance). This does not require large power in order to change in phase at high speed, thereby reducing the produced vibrations. Therefore, a simple motor can be used to perform the phase control at high speed and to maintain sufficiently high mechanical reliability.
Preferably, the rotation axis of the rotator is positioned substantially parallel to the conductive strip, thereby increasing the effect of the phase change as the rotator comes closer to the conductive strip.
A phase shifter according to the present invention may include two substantially planar conductive plates, a dielectric strip sandwiched between the two conductive plates, and a rotator at least partially including a conductor or a dielectric, the rotator being positioned at at least one side of the dielectric strip so as to freely rotate while the rotation axis of the rotator is substantially parallel to the conductive strip.
Therefore, the two conductive plates, and the dielectric strip sandwiched therebetween can form a dielectric line. As the distance from the conductor or dielectric positioned at either side of the dielectric strip to the dielectric strip, or the opposing areas changes, the phase constant of the dielectric line changes, thereby changing the phase of a transmission signal. The signal propagating on the transmission line changes in phase as the rotator rotates, and a large amount of power is not required to change phase at high speed, as previously described. Therefore, a simple motor can be used to perform the phase control at high speed and to maintain sufficiently high mechanical reliability. Since the rotator is positioned at either side of the dielectric strip, the overall thickness of the dielectric strip sandwiched between the two conductive plates can be reduced. The rotator may also be positioned at the two sides of the dielectric strip, thereby maintaining a large amount of phase shift.
Preferably, the rotation axis of the rotator is positioned substantially in parallel to the dielectric strip, thereby increasing the effect of the phase change as the rotator comes closer to the dielectric strip.
The rotator of the phase shifter may have a predetermined conductive pattern formed on a surface of a tubular or cylindrical dielectric base, and can thus be simplified. The conductive pattern formed on the surface allows a variety of phase-shift patterns as the rotator rotates. Alternatively, the rotator may be formed of a conductive member having a predetermined shape. The rotator can thus be easily produced. Variations of characteristics can also be reduced.
In another aspect of the present invention, a phased-array antenna includes a ground electrode formed on the above-described dielectric plate on which a conductive strip is formed, and a plurality of slots formed in the ground electrode, through which electromagnetic waves are emitted.
Therefore, a transmission line formed of the conductive strip can serve as a feed line for the slot antennas. The phase constant of the transmission line changes as the rotator rotates, thereby causing a change in feed phase with respect to the slot antennas, resulting in beam scanning. The phased-array antenna can therefore be constructed with a simplified overall structure. In addition, even if beam scanning is performed at high speed, the inertia resistance or vibrations can be reduced. Therefore, a simple motor can be used to perform the phase control at high speed with ease and to maintain sufficiently high mechanical reliability.
In another aspect of the present invention, a phased-array antenna includes microstrip antenna patches formed on the above-described dielectric plate on which a conductive strip is formed. Therefore, a line formed of the conductive strip can serve as a feed line for the aligned microstrip antenna patches. The phase constant of the line changes as the rotator rotates, thus causing a change in feed phase with respect to the microstrip antenna patches. The phased-array antenna can therefore be constructed with a simplified overall structure. In addition, even if beam scanning is performed at high speed, the inertia resistance or vibrations can be reduced. Therefore, a simple motor can be used to perform the phase control at high speed with ease and to maintain sufficiently high mechanical reliability.
In another aspect of the present invention, a phased-array antenna includes a plurality of slots formed in the conductive plate. Therefore, the slots can serve as slot antennas, and the dielectric line can serve as a feed line for the slot antennas. The rotation of the rotator causes a change in feed phase with respect to the slot antennas, resulting in beam scanning. The phased-array antenna can therefore be simple, compact, and lightweight.
In another aspect of the present invention, a radar includes any of the above-described phased-array antennas, and a transceiver using the phased-array antenna for transmission and reception. The radar can thus perform high-speed scanning and can be highly shock-resistant. In addition, a simple motor can be used to perform the phase control at high speed and to maintain sufficiently high mechanical reliability.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.